Wednesday, December 2, 2009

ACID RAIN -IGCSE/GCSE CHEMISTRY NOTES

2) Fossil fuels are burnt on a huge scale - Acid Rain.
Coal (and to a lesser degree Oil and Natural Gas) contain sulphur.When they are burnt the sulfur oxidises (reacts with oxygen)to form sulfur dioxide gas.
sulfur + oxygen sulphur dioxide.
S(s) + O2(g) SO2(g)
Sulfur dioxide gas is acidic, poisonous, and smells of bad eggs.It is removed from the burnt waste gases and used in the contact process.If it gets into the atmosphere it reacts with water and oxygen in the airto form a dilute solution of sulfuric acid.This sulfuric acid is the main pollutant in acid rain.Natural rain is slightly acidic due to dissolved carbon dioxide.Natural rain has a pH of 5·5, acid rain has a pH of
4.The second most important pollutant in acid rain is nitric acid - see next page.
Acid rain kills trees.It runs into rivers and gathers in lakes.Eventually, lakes become too acidic, and plants and fish begin to die.Acid rain reacts with limestone and damages limestone buildings.
Powdered limestone or slaked lime can be added to soils or lakesto make them less acidic. It would be better if we could avoid or reducepollutant gas emissions in the first place.

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